Minority electron mobility and lifetime in the p+GaAs base of AlGaAs/GaAs heterojunction bipolar transistors

Abstract

AlGaAs/GaAs heterojunction bipolar transistors with different base doping concentrations grown by gas source molecular beam epitaxy were fabricated and characterized at dc and high frequency. Three different base doping concentrations; 5×1018, 1×1019, and 5×1019 cm-3 doped with Be were used for the characterization with the same structural and process parameters, including 0.2 μm base width. Minority electron mobilities in heavily doped p type were measured as 1.1×103, 1.3×103, and 3×103 cm2 V/s for 5×1018, 1×1019, and 5×1019 cm-3, respectively, by using the current gain cutoff frequency (fT) which agrees well with theoretical predictions in heavily doped p-type GaAs. Combining dc and high frequency measurements, electron lifetimes of 1.2×10 -9, 5.5×10-10, and 2×10-11 s have been obtained for these three dopings, respectively.